The phosphoproteins DARPP-32 and ARPP-21 are substrates for cyclic AMP- dependent protein kinase, and their concentration is highly enriched in the majority of D1-dopaminoceptive neurons of the basal ganglia. The long-term objective of this proposal is to elucidate the genetic and epigenetic factors which regulate the development of these D1-dopaminoceptive neuronal phenotypes. Genomic clones for DARP-32 and ARPP-21 will be isolated and the structure and function of the 5'-regulatory regions will be studied. Primer extension and S2-nuclease analysis will be used to determine the transcription start sites. Transient transfection assays of cell lines or of primary striatal cell cultures will be used to identify proximal promoter and distal enhancer regions. Gel-shift and DNA footprinting assays will be used to determine whether DNA sequences from the two genes bind the same nuclear proteins. Finally, the accumulation of DARPP-32 and ARPP-21 will be examined in a dissociated cell culture system, varying defined parameters known to influence the development of other neuronal phenotypes, including cell density, astroglia, depolarization, and concentrations of glutamate and insulin. These experiments are expected to eventually lead to the identification of caudate-specific nuclear transcription factors, and extracellular conditions required for the normal development of the D1-dopaminoceptive phenotype. Dysfunction of the nigrostriatal and mesocortical dopamine systems is implicated in several brain diseases, including schizophrenia, Parkinson's Huntington's and developmental cognitive disorders. Although the primary causes are poorly understood, a mainstay of treatment is frequently pharmacological manipulation of the dopaminergic system. Knowledge of the basic mechanisms underlying determination of the dopaminoceptive neuronal phenotype may provide important new clues to the pathophysiology and pharmacotherapy of these diseases.